This invention relates to a sheet feeding apparatus for feeding porous sheets of media from a stack of such sheets.
The applicant has developed various printheads which provide high speed, photographic quality printing. The printheads comprise ink jet nozzles arranged in a close packed array. To provide the photographic quality printing, the nozzles are so arranged so as to provide a resolution of up to 1600 dots per inch (dpi).
The ink jet nozzles are formed using microelectromechanical systems (MEMS) technology. The use of MEMS technology results in very high speed printing capabilities where pages can be printed at a rate of up to 2 pages per second (for double-sided printing). To facilitate such high speed printing, it is important, firstly, that the paper or print media fed to the printing station of the printer is accurately aligned and capable of the required feed rate with as little likelihood as possible of paper jams or the like occurring. Secondly, the paper must be able to be fed to the printing station at a rate sufficient to use the high speed printing capabilities of the printing station to its fullest extent.
According to a first aspect of the invention there is provided a sheet feeding apparatus for feeding porous sheets from a stack, the apparatus comprising
an air displacement device having an outlet conduit;
at least one outlet nozzle connected to the outlet conduit, the, or each, outlet nozzle being displaceable between a pick-up position proximate a first sheet of the stack and a feed position, the air displacement device being configured to generate a flow of air from the, or each, outlet nozzle sufficient to penetrate the first sheet such that a cushion of air is generated between the first sheet and a second sheet to lift the first sheet from the second sheet;
an air extraction device having an inlet conduit;
at least one inlet nozzle connected to the inlet conduit, the, or each, inlet nozzle defining a pick-up surface and being displaceable between a pick-up position proximate a first sheet of the stack and a feed position, the air extraction device being configured to generate a flow of air into the, or each, inlet nozzle such that the first sheet is drawn against the pick-up surface;
a reciprocal drive mechanism for driving the inlet and outlet nozzles reciprocally between the pick-up position and the feed position; and
a feed mechanism that is arranged with respect to the inlet and outlet nozzles so that, when the nozzles are driven into the feed position, the feed mechanism engages the first sheet.
The apparatus may include a plurality of outlet nozzles that are positioned to span the first sheet, a plurality of inlet nozzles, also positioned to span the first sheet, an outlet manifold that interconnects the outlet conduit of the air displacement device and the outlet nozzles and an inlet manifold that interconnects the inlet conduit of the air extraction device and the inlet nozzles.
The inlet and outlet nozzles may be generally aligned and may be in alternating positions with respect to each other.
The air displacement mechanism may be an air pump and the air extraction device may be an evacuation pump. Both pumps may be connected to a shaft of the drive motor so that, when operated, the air pump serves to supply air to the outlet conduit and the evacuation pump serves to draw air into the inlet conduit substantially simultaneously.
A flexible hose may interconnect each nozzle with its respective manifold, thereby facilitating displacement of the nozzles with respect to their respective manifolds.
The nozzles may be connected to an elongate carrier, which, in turn, may be connected to the reciprocal drive mechanism so that the elongate carrier and thus the nozzles can be displaced reciprocally between the pick-up and feed positions.
The elongate carrier may be a bar and the drive mechanism may include a stepper motor connected to an axle that extends substantially parallel to the bar. A swing arm may be interposed between each end of the axle and a corresponding end of the bar so that reciprocal movement generated by the stepper motor can be transmitted to the bar and thus the nozzles.
Each nozzle may have a sheet-engaging member that, in respect of the inlet nozzles, defines the pick-up surfaces and, in respect of the outlet nozzles is such that as air is expelled from the outlet nozzles, a region of low pressure is generated intermediate the outlet nozzle and the first sheet, thereby facilitating lifting of the first sheet.
The feed mechanism may be in the form of a roller assembly.
The invention extends to a printer which includes a sheet feeding apparatus as described above.
According to a second aspect of the invention, there is provided an apparatus for separating a sheet of print media from a stack of sheets, the sheets of the stack being porous and the apparatus including:
a sheet conveying means for conveying a topmost sheet of print media, which has been separated from the stack, to a printing station of a printer;
a separating means, associated with the sheet conveying means for separating the sheet of print media from the stack, the separating means including a fluid delivery means for blowing fluid on to a top surface of the stack for effecting separation of the topmost sheet of print media from the stack; and
a capturing means, carried by the sheet conveying means, for capturing at least a part of said topmost sheet and for facilitating conveyance of said topmost sheet by the sheet conveying means to the printing station.
The sheet conveying means may comprise a picker assembly for picking the topmost sheet from the stack. The picker assembly may comprise an elongate element in the form of a bar or tube and a plurality of displacement assistance means for assisting in displacement of the topmost sheet from the stack, the displacement assistance means being arranged at spaced intervals along a length of the elongate element. A further embodiment of the present invention provides a sheet separator apparatus for separating a sheet of print media from a stack of sheets, the sheets of the stack being porous and the sheet separator including:
a conveyor that conveys a topmost sheet of print media which has been separated from the stack to a printing station of a printer;
at least one fluid outlet providing a fluid flow through a top surface of the stack for effecting separation of the topmost sheet of print media from the stack; and
a pick up device, carried by the conveyor, that captures at least a part of said topmost sheet and aids conveyance of said topmost sheet by the sheet conveyor to the printing station.
The elongate element may define a plurality of fluid ports and each displacement assistance means may comprise a footprint-defining portion surrounding one of the ports and depending from the elongate element. More particularly, each displacement assistance means may be in the form of a pad or disc which depends from the elongate element towards the stack, in use. Each pad may depend from a hollow stalk which is received in one of the fluid ports of the elongate element. The stalk may define a passage.
The fluid delivery means may comprise a plurality of fluid supply conduits, each conduit being in fluid communication with one of the fluid ports of the elongate element, only certain of the fluid ports having fluid supply conduits associated with them with a remainder of the fluid ports not being in fluid communication with the fluid supply conduits.
The fluid supply conduits may be connected to, and communicate with, a fluid supply manifold.
The capturing means may be a fluid suction arrangement, the capturing means comprising a plurality of fluid suction conduits, each fluid suction conduit being in fluid communication with one of the remainder of the fluid ports of the elongate element.
The fluid suction conduits may be connected to, and communicate with, a fluid extraction manifold.
The picker assembly is operable to lift the topmost sheet from the stack and to feed it to the printing station. A pair of pinch rollers may be arranged at an input to the printing station. In a preferred embodiment, the bar of the picker assembly is mounted on a pair of spaced swing arms and pivots relative to the swing arms. The swing arms, in turn, are fixedly mounted on an axle which is rotatably supported on the printer. Accordingly, to facilitate movement of the bar of the picker assembly, the fluid supply conduits and the fluid suction conduits may be in the form of flexible hoses.
The apparatus may comprise a fluid supply means for supplying a fluid to the fluid supply manifold for supply to the fluid supply conduits and a fluid extraction means for extracting fluid from the fluid extraction manifold to create a suction effect in the fluid suction conduits. The apparatus may further comprise a drive means for driving the fluid supply means and the fluid extraction means. The fluid supply means and the fluid extraction means may each be in the form of an air pump and extraction pump, respectively.
The drive means may be a drive motor. The air pump may be mounted on a first output shaft of the drive motor with the extraction pump being mounted on an opposed, second output shaft of the drive motor.
The apparatus may further comprise a control means for controlling supply of fluid to the fluid supply manifold and extraction of fluid from the fluid extraction manifold. The control means may comprise a valve arranged in each of the fluid supply manifold and the fluid extraction manifold. Preferably, each valve is electromagnetically operated. More particularly, each valve may be in the form of a solenoid valve arranged in an inlet opening of the fluid supply manifold and an outlet opening of the fluid suction manifold.